1. Technical Field
The present invention generally relates to wireless communication systems and in particular to transmission scheduling in wireless communication systems.
2. Description of the Related Art
In wireless communication systems employing packet-scheduling, part of the air-interface resources are assigned dynamically to different mobile stations (MS). In an orthogonal frequency division multiple access (OFDMA) system, these dynamically allocated resources, which comprise multiple subcarriers (subbands), are dynamically shared between multiple MSs. According to the Long Term Evolution (LTE) standard, the user equipment (UE) is configured to report Channel Quality Indicators (CQIs) to assist the Evolved Node B (eNodeB) in selecting an appropriate modulation code scheme (MCS) to use for downlink transmissions. CQI information is reported from user equipment to a base station so that the base station can perform an appropriate scheduling of radio resources in consideration of the channel quality indicator in a downlink shared data channel. The CQI reports are derived from the downlink received signal quality, typically based on measurements of the downlink reference signals. In LTE, physical uplink control channel (PUCCH), which carries control information via uplink transmission towards the evolved Node B (eNodeB), is used for reporting the CQI information.
In current frequency selective scheduling (FSS) techniques for LTE, subband CQI reports are being used by the FSS in deciding user equipment-physical resource block (UE-PRB) combinations. However, because of the reporting mechanism used, each subband does not report a subband CQI value at each reporting sub-frame. Furthermore, a subband CQI value for one or more subbands may not be reported for several consecutive reporting sub-frames. As a result, inaccuracies in subband CQIs due to old/“stale” subband CQI values/reports may result in poor scheduler performance.